Hydroxyl-Radical Kinetics by Kinetic Spectroscopy. II. Reactions with C2H6, C3H8, and iso-C4H10 at 300°K

Gas‐phase, room‐temperature reactions of the OH radical with C₂H₆, C₃H₈, and iso‐C₄H₁₀ were studied with the flash‐photolysis—kinetic‐spectroscopy (KS) technique. Rate constants (in units of cubic centimeters per mole·second) were obtained as follows: $${\mathrm{C}}_2{\mathrm{H}}_6+\mathrm{OH}\to {\mathrm{C}}_2{\mathrm{H}}_5+{\mathrm{H}}_2\mathrm{O}{\mathrm{,\hspace{0.17em}\hspace{0.17em}k}}_3{\text{=1.76±0.23×10}}^{11}\hspace{0.17em}\mathrm{at}{\text{\hspace{0.17em}302}}^{\circ }{\text{±2}}^{\circ }\mathrm{K},$$ $${\mathrm{C}}_3{\mathrm{H}}_8+\mathrm{OH}\to {\mathrm{C}}_3{\mathrm{H}}_7+{\mathrm{H}}_2\mathrm{O}{\mathrm{,\hspace{0.17em}\hspace{0.17em}k}}_4{\text{=8.2±1.2×10}}^{11}\hspace{0.17em}\mathrm{at}{\text{\hspace{0.17em}298}}^{\circ }{\text{±1}}^{\circ }\mathrm{K},$$ $$\mathrm{iso}{\mathrm{-C}}_4{\mathrm{H}}_{10}+\mathrm{OH}\to {\mathrm{C}}_4{\mathrm{H}}_9+{\mathrm{H}}_2\mathrm{O}{\mathrm{,\hspace{0.17em}\hspace{0.17em}k}}_5{\text{=1.28±0.07×10}}^{12}\hspace{0.17em}\mathrm{at}{\text{\hspace{0.17em}297}}^{\circ }{\text{±1}}^{\circ }\mathrm{K}.$$ It is shown that relative theoretical values for frequency factor ratios and Evans—Polanyi activation energies are inconsistent with the ratios of the observed rate constants for H abstraction by OH from these alkanes.